Right now I am working with expression checkout.
I got two properties in API one is return url and other one is callback url.
I know about return url but when to use callback url?
In case of recurring payments which one is better to use to acknowledge of transaction?
The ReturnURL is where PayPal will redirect the user after they’ve completed their review/payment on the PayPal pages.
CallbackURL is used to direct PayPal to a web service that you have setup which can receive the payer’s shipping information from PayPal’s server, generate shipping and sales tax rates based on that data, and return shipping options back to the PayPal review screen. This populates the drop-down on this review page with your returned rates so the buyer can choose from those during the PayPal review and eliminate the additional step once they return to your site.
In theory, it’s great, but unfortunately, I haven’t had good experience with it. It does work, but it only gives the application a max of 6 seconds to complete everything. If you’re attempting to call out to 3rd party services like UPS, USPS, FedEx, etc. within your callback script in order to obtain rate information, this will generally chew up all that time and PayPal will default to the shipping options you provided with your SetExpressCheckout request.
If you have a real quick method of obtaining shipping rates, though, it’s a great system.